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BAtteries occasionally in parallel with DC "Charging" source? — Parallax Forums

BAtteries occasionally in parallel with DC "Charging" source?

xanatosxanatos Posts: 1,120
edited 2013-12-31 09:54 in General Discussion
I have an application that is normally powered by batteries in the field. Due to various temperature and user issues, occasionally, it may be preferable to use a wall wart DC supply to power the unit. Usually this would be in the range of 30 minutes or less.

The wall wart would replace the battery power. I know that:

Normally, I would want to use a diode to block "charging" current to the alkaline cells, since they don't seem to play well with any charging current - but that would also diminish the supply current from those batteries to the circuit when running on batteries.

I could also use a power jack that switched out the batteries when the wall wart was plugged in.

But I was just wondering what the experienced in here have to say about such an arrangement. Do alkalines really blow up and squirt their guts out if exposed to a charging current for a half an hour or so?

Just curious.

Thanks...

Comments

  • kwinnkwinn Posts: 8,697
    edited 2013-12-30 21:49
    xanatos wrote: »
    I have an application that is normally powered by batteries in the field. Due to various temperature and user issues, occasionally, it may be preferable to use a wall wart DC supply to power the unit. Usually this would be in the range of 30 minutes or less.

    The wall wart would replace the battery power. I know that:

    Normally, I would want to use a diode to block "charging" current to the alkaline cells, since they don't seem to play well with any charging current - but that would also diminish the supply current from those batteries to the circuit when running on batteries.

    I could also use a power jack that switched out the batteries when the wall wart was plugged in.

    But I was just wondering what the experienced in here have to say about such an arrangement. Do alkalines really blow up and squirt their guts out if exposed to a charging current for a half an hour or so?

    Just curious.

    Thanks...

    Depends on how much higher the voltage of the wall wart is and how much current it could supply. The switching jack would be the simplest, but you might be able to use a schottky diode in some cases.
  • lanternfishlanternfish Posts: 366
    edited 2013-12-30 22:10
    xanatos wrote: »
    ...

    The wall wart would replace the battery power. I know that:

    Normally, I would want to use a diode to block "charging" current to the alkaline cells ... but that would also diminish the supply current from those batteries to the circuit when running on batteries. ...

    A diode would drop the voltage from the batteries by approx 1 volt but wouldn't affect the current unless of course the circuit drew more current than the diode can handle in which case ... Phtttt ... And no current will flow :-(

    Is it worth replacing/possible to replace the alkalines with some rechargeable batteries and a small charging/switching ?

    Happy 2014
  • al1970al1970 Posts: 64
    edited 2013-12-30 23:34
    Hi:

    Just use a transistor and you won't get the .6 volt voltage drop.
  • Hal AlbachHal Albach Posts: 747
    edited 2013-12-31 09:54
    I'm using a 1N5819 Schottky diode to protect a Li coin battery and when conducting the forward drop is 0.07 - 0.09 with a current of approx 7 micro Amps.
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